Biosynthesis of antibiotics in a number of structural classes will be investigated, using potential precursors and intermediates labeled with radioactive and stable isotopes, as well as mutant strains and protoplasts of the producing microorganisms. Antibiotics to be studied include aminocyclitols (neomycin), antibiotics containing a shikimate-related C7N unit (pactamycin, validamycin, the ansamycins geldanamycin and streptovaricin), peptides (berninamycin, emerimicin), and acyltetramic acids (streptolydigin). Mutasynthesis, the technique developed in our laboratory, will be used to prepare new antibiotics related to neomycin, novobiocin, and perhaps, pactamycin, some of which should have therapeutic properties improved over those of the parent antibiotic. Chemical synthesis will be employed in attempts to convert streptovaricin to modified antibiotics related to rifampicin. Inhibitors of bacterial RNA polymerase and terminal deoxyribonucleotidyltransferase will be synthesized in radioactive form from streptovaricins and acyltetramic acids.